In view of a problem of petroleum exhaustion, it is recently proposed to perform gasification using petroleum coke which is a residue in petroleum refinement, low-quality coal or other fossil fuel such as oil sand, bitumen or lignite which is not effectively used as resource at present, biomass or tire chips as raw material to acquire and effectively utilize a gasification gas comprising hydrogen, hydrocarbon and the like. A circulating fluidized bed gasification furnace is disclosed in Patent Literature 1.
FIG. 1 is a schematic of a circulating fluidized bed gasification furnace represented by Patent Literature 1 and having a combustion furnace 1 (fluidized combustion furnace) for combustion of char with air 2 to heat a circulating medium. A combustion exhaust gas 3 from the combustion furnace 1 is introduced into a cyclone collector 4 where the circulating medium 5 is captured and an exhaust gas 6 is discharged. The captured circulating medium 5 is supplied through a downcomer 7 to a fluidized bed gasification furnace 8 while a gasifying agent 9 such as steam or air is supplied to a lower portion of the furnace 8 to form a fluidized bed 10. A raw material 12 is supplied to a freeboard 11 of the fluidized bed gasification furnace 8 to gasifying the raw material 12 into a gasification gas 13. The circulating medium 5 and char or unreacted solid not gasified in the fluidized bed gasification furnace 8 are returned through a circulation flow passage 14 to the combustion furnace 1 so as to burn the char.
The fluidized bed gasification furnace 8 shown in FIG. 1, which produces the highly combustible gasification gas 13, includes a sealer 15 comprising for example a U-shaped duct which blocks gas movement between the combustion and gasification furnaces 1 and 8. The downcomer 7 connected to the cyclone collector 4 has a lower end providing a sealer 16 which blocks gas movement by forming a connection such that the circulating medium 5 from the collector 4 is supplied into the fluidized bed 10 in the fluidized bed gasification furnace 8. For the sealers 15 and 16, a gasification chamber and a seal chamber connected to allow movement of the circulating medium within the fluidized bed 10 may be arranged in the fluidized bed gasification furnace 8, the circulation flow passage 14 or the lower end of the downcomer 7 being connected to the seal chamber.
In the above-mentioned circulating fluidized bed gasification furnace, the raw material 12 is supplied to the fluidized bed gasification furnace 8 by an on-bed supply mode where the raw material is supplied to the freeboard 11 on the fluidized bed 10 in the gasification furnace 8 as shown in FIG. 1 or by an in-bed supply mode where the raw material is supplied into the fluidized bed 10 in the furnace 8.
Devices representative of the in-bed supply mode include those using a screw feeder to press and supply a raw material into the fluidized bed in the combustion furnace (see, e.g., Patent Literatures 2 and 3).